InAs Nanowire Josephson Field Effect Transistors

We have fabricated superconducting nano-junctions using InAs nanowires contacted with Al superconducting electrodes. The diameter of nanowire is about 70 nm with source-drain spacing of 200 nm. Low Ohmic metallic contacts are formed at the interface with typical $R_{N}A$ value of $3\times 10^{-7}$ $\Omega$ cm$^{2}$. Below the superconducting transition temperature $T_{C} =1.1$ K, the devices show clear conductance enhancements below the superconducting gap $2\Delta_{0} = 210$ $\mu$eV, which is explained by multiple Andreev reflection. Near zero-bias voltage, conductance diverges to show supercurrent in V(I) curve. Maximum critical current is about $I_{C} = 130$ nA at T = 30 mK with $I_{C}R_{N}$ product of 60 $\mu$V. Irradiated with microwave, constant voltage plateaus are observed satisfying ac Josephson relation. By applying back-gate voltage, critical currents are suppressed to be zero near pinch-off gate voltage $V_{g}$ = -70 V. Universal conductance fluctuations of nanowire and its corresponding critical current fluctuations are discussed from the viewpoint of truly mesoscopic Josephson field effect transistors.